The present invention relates to all solid-state batteries.
Many proposals have heretofore been made for lithium batteries of high energy density wherein the electrolyte is a nonaqueous solvent of high ion conductivity, the negative electrode active substance is lithium, and the positive electrode active substance is a substance having high electron conductivity and voids capable of accepting many lithium ions. Especially, a strong demand has been made in recent years for the type or form of batteries in respect of compactness, lightweightness, reduced thickness, etc., with demand also made for amenability to high-temperature ambient conditions or superhigh vacuum ambient conditions. To meet these demands, improvements have been made in liquid electrolytes which have been the greatest problem, with efforts devoted to the development of solid electrolytes with no boiling point or no vapor pressure. Active research is presently under way on high polymer materials which can be adhered completely to the negative electrode material and to the positive electrode material at the interface of adhesion, and which are capable of giving flexibility to the interface of adhesion. For example, heretofore proposed as such high polymer solid electrolytes are polyethylene oxide (PEO) and polypropylene oxide (PPO) compounds in JP-B-3422/1988, "CHARGEABLE ELECTROCHEMICAL POWER GENERATOR," polyphenylene oxide, polysulfone and polyvinylidene chloride compounds in JP-B-30807/1975, "SOLID ELECTROLYTE FILM," N-alkoxymethyl nylon compounds in JP-B-45797/1976, "SEMI-SOLID ELECTROLYTE," and pyridine-pyrrole compounds in JP-A-49490/1977, "PROCESS FOR PREPARING LITHIUM ION CONDUCTIVE SOLID ELECTROLYTE." Further polyphosphazene compounds are proposed in J. Am. Chem. Soc., Vol. 106, 6854.about.6855 (1984).
However, these proposed high polymer solid electrolytes have problems. First, they are too low in ion conductivity for use as electrolytes in lithium batteries which are actually usable. Even the highest of the ion conductivities of the proposed high polymer solid electrolytes is 10.sup.-5 .about.10.sup.-6 S/cm. The conductivity is as low as 10.sup.-6 .about.10.sup.-7 S/cm especially at room temperature. Second, they are very low in the transportation value of the mobile cation Li.sup.+. The proposed high polymer solid electrolyte is of the biionic type wherein both dissociated cation and anion of an inorganic lithium salt dissolving in the electrolyte move toward the positive electrode and the negative electrode at the same time, so that the transportation value of Li.sup.+ becomes small. Accordingly, when the proposed high polymer solid electrolytes are used for fabricating lithium batteries, the batteries obtained are only those of poor charge-discharge characteristics which give only a low current of small current density.
An object of the present invention is to overcome the foregoing problems and provide an all solid-state battery which is small-sized and lightweight and which has a large charge-discharge capacity and outstanding characteristics.